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Ch14 lecture 3e

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Ch14 lecture 3e Ch14 lecture 3e Presentation Transcript

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  • This lecture will help you understand:
    • Environmental health hazards
    • Toxicants in the environment
    • Hazards and their effects
    • Risk assessment and risk management
    • Philosophical approaches to risk
    • Policy and regulation in the U.S. and internationally
  • Central Case: Lake Apopka alligators
    • Alligators in Lake Apopka, Florida, had reproductive problems
    • The lake had high levels of agricultural runoff
    • Chemical contaminants were disrupting the endocrine systems of alligators during egg development
    • Because alligators and humans share the same hormones, chemicals can affect people, too
  • There are many types of environmental hazards
    • Environmental health = assesses environmental factors that influence human health and quality of life
      • Natural and human-caused factors are both considered
    • Physical hazards = occur naturally in our environment
      • Earthquakes, volcanoes, fires, floods, droughts
      • We can’t prevent them, but we can prepare for them
      • We increase our vulnerability by deforesting slopes (landslides), channelizing rivers (flooding), etc.
      • We can reduce risk by better environmental choices
  • Chemical and biological environmental hazards
    • Chemical = synthetic chemicals such as pesticides, disinfectants, pharmaceuticals
      • Harmful natural chemicals also exist
    • Biological = result from ecological interactions
      • Viruses, bacteria, and other pathogens
      • Infectious ( communicable , or transmissible ) disease = other species parasitize humans, fulfilling their ecological roles
      • We can’t avoid risk, but we can reduce the likelihood of infection
  • Cultural environmental hazards
    • Cultural = result from the place we live, our socioeconomic status, our occupation, our behavioral choices
      • Smoking, drug use, diet and nutrition, crime, mode of transportation
  • Four types of environmental hazards
  • Disease is a major focus of environmental health
    • Despite our technology, disease kills most of us
    • Disease has a genetic and environmental basis
      • Cancer, heart disease, respiratory disorders
      • Poverty and poor hygiene can foster illnesses
  • Infectious diseases kill millions
    • Infectious diseases kill 15 million people per year
      • Half of all deaths in developing countries
      • Developed countries have better hygiene, access to medicine, and money
    • Vector = an organism that transfers pathogens to a host
  • Many diseases are increasing
    • Tuberculosis, acquired immunodeficiency syndrome (AIDS), and the West Nile virus
    • Our mobility spreads diseases
    • Diseases are evolving resistance to antibiotics
    • Climate change will expand the range of diseases
    • To predict and prevent diseases, experts deal with complicated interrelationships
  • Environmental health hazards exist indoors
    • Radon = a highly toxic, radioactive gas that is colorless and undetectable
      • Can build up in basements
    • Lead poisoning = from lead pipes
      • Damages organs; causes learning problems, behavior abnormalities, and death
    • Asbestos = insulates, muffles sounds, and resists fire
      • Asbestosis = scarred lungs may cease to function
  • A recently recognized hazard
    • Polybrominated diphenyl ethers (PBDEs) = has fire-retardent properties
      • Used in computers, televisions, plastics, and furniture
      • Persist and accumulate in living tissue
      • Endocrine disruptors = compounds that mimic hormones and interfere with the functioning of animals’ endocrine (hormone) systems
      • Affect brain and nervous system development, and may cause cancer
  • Toxicology is the study of poisonous substances
    • Toxicology = the study of the effects of poisonous substances on humans and other organisms
    • Toxicity = the degree of harm a toxicant can cause
      • “ The dose makes the poison” = toxicity depends on the combined effect of the chemical and its quantity
      • Analogous to pathogenicity or virulence = the degree of harm of biological hazards that spread disease
    • Toxicant = any toxic agent
  • Environmental toxicology
    • Deals with toxic substances that come from or are discharged into the environment
    • Studies the health effects on humans, other animals, and ecosystems
      • Focus mainly on humans, using other animals as test subjects
      • Can serve as indicators of health threats
    • Don’t forget, chemicals have given us our high standard of living
  • Toxic agents in the environment
    • The environment contains countless natural chemicals that may pose health risks
    • But, synthetic chemicals are also in our environment
      • Every human carries traces of industrial chemicals
    80% of U.S. streams contain at least trace amounts of 83 wastewater contaminants
  • Very few chemicals have been thoroughly tested
    • 100,000 chemicals are on the market today
      • 72,000 industrial
      • 8,700 food additives
      • 2,000 new chemicals introduced per year
    • We don’t know the effects, if any, they have
  • Silent Spring began public debate over chemicals
    • Rachel Carson published Silent Spring in 1962
      • Brought together studies to show DDT risks to people, wildlife, and ecosystems
      • In the 1960s, pesticides were mostly untested and were sprayed over public areas, assuming they would do no harm
    • The book generated significant social change
  • Types of toxicants
    • Carcinogens = cause cancer
    • Mutagens = cause DNA mutations
      • Can lead to severe problems, including cancer
    • Teratogens = cause birth defects
    • Allergens = overactivate the immune system
    • Neurotoxins = assault the nervous system
    • Endocrine disruptors = interfere with the endocrine (hormone) system
  • Endocrine disruption may be widespread
    • Theo Colburn wrote Our Stolen Future in 1996
      • Synthetic chemicals may be altering the hormones of animals
      • This book integrated scientific work from various fields
      • Shocked many readers and brought criticism from the chemical industry
  • Evidence for hormone disruption
    • Frogs also have gonadal abnormalities
      • Male frogs became feminized from atropine concentrations well below EPA guidelines
    • PCB-contaminated human babies were born weighing less, with smaller heads
  • Male sperm counts are dropping
    • Scientists attribute the shocking drop in men’s sperm counts to endocrine disruptors
      • The number and motility of sperm has dropped 50% since 1938
    • Testicular cancer, undescended testicles, and genital birth defects are also increasing
  • Endocrine disruption research is controversial
    • Research results are uncertain, which is inherent in any young field
    • Negative findings pose economic threats to chemical manufacturers
      • Banning a top-selling chemical could cost a company millions of dollars
      • Bisphenol-A, found in plastics, can cause birth defects, but the plastics industry protests that the chemical is safe
    • Studies reporting harm are publicly funded, but those reporting no harm are industry funded
  • Toxins may concentrate in water
    • Runoff carries toxins from large land areas to small volumes of surface water
    • Chemicals can leach into the soil
    • Chemicals enter organisms through drinking or absorption
      • Aquatic organisms are effective pollution indicators
  • Routes of chemical transport
  • Airborne toxicants travel widely
    • Because chemicals can travel by air, their effects can occur far from the site of chemical use
    • Pesticide drift = airborne transport of pesticides
    • Synthetic chemical contaminants are found globally
      • They appear in arctic polar bears, Antarctic penguins, and people living in Greenland
  • Some toxicants persist for a long time
    • Toxins can degrade quickly and become harmless
      • Or, they may remain unaltered and persist for decades
      • Rates of degradation depends on temperature, moisture, and sun exposure
    • Persistent chemicals have the greatest potential for harm
    • Breakdown products = toxicants degrade into simpler products
      • May be more or less harmful than the original substance
      • DDT degrades into DDE, which is also highly persistent
  • Toxicants can accumulate and biomagnify
    • Some toxicants can be excreted or metabolized
      • Fat-soluble toxicants are stored in fatty tissues
    • Bioaccumulation = toxicants build up in animal tissues
    • Biomagnification = toxicants concentrate in top predators
      • Near extinction of peregrine falcons and brown pelicans
  • Not all toxicants are synthetic
    • Chemical toxicants also exist naturally and in our food
      • Don’t assume natural chemicals are all healthy and synthetic ones are all harmful
    • Some scientists feel that natural toxicants dwarf our intake of synthetic chemicals
      • Natural defenses against toxins are effective against synthetic ones, too
      • Critics say natural toxins are more readily metabolized and excreted, and synthetic chemicals persist and accumulate
  • Wildlife studies
    • Museum collections provide data from times before synthetic chemicals were used
    • Measurements from animals in the wild can be compared to controlled experiments in the lab
    • Scientists can first measure effects in the lab, then look for correlations in the wild
    • Conspicuous mortality events can trigger research
      • Many sea otters died and washed ashore
      • Research showed they died from parasites carried in sewage runoff containing cat litter
  • Human studies
    • Case histories = studying sickened individuals directly
      • Autopsies
      • Don’t tell about future risks
    • Epidemiology = large-scale comparisons between groups of people
      • Studies between exposed and unexposed people last for years
      • Yield accurate predictions about risk
    • Animals are used as test subjects
      • Some people object to animal research
      • New techniques (human cell cultures, bacteria, etc.) may replace some live-animal testing
  • Dose-response analysis
    • Dose-response analysis = measuring how much effect a toxicant produces at different doses
      • Animal testing
      • Dose = the amount of toxicant the test animal receives
      • Response = the type or magnitude of negative effects of the animal
      • Dose-response curve = the plot of dose given against response
  • Dose response curves
    • LD 50 /ED 50 = the amount of toxicant required to kill (affect) 50% of the subjects
    • Threshold = the dose level where certain responses occur
      • Organs can metabolize or excrete low doses of a toxicant
      • Some toxicants show a J-shaped, U-shaped, or inverted curve
    • Scientists extrapolate downward from animal studies to estimate the effect on humans
      • Regulatory agencies set allowable limits well below toxicity levels in lab studies
  • Individuals vary in their responses to hazards
    • Different people respond differently to hazards
      • Affected by genetics, surroundings, etc.
      • People in poor health are more sensitive
      • Sensitivity also varies with sex, age, and weight
      • Fetuses, infants, and young children are more sensitive
    • Standards for responses are set by the Environmental Protection Agency (EPA)
      • Often, standards are not low enough to protect babies
  • The type of exposure affects the response
    • Acute exposure = high exposure for short periods of time to a hazard
      • Easy to recognize
      • Stem from discrete events: ingestion, oil spills, nuclear accident
    • Chronic exposure = low exposure for long periods of time to a hazard
      • Hard to detect and diagnose
      • Affects organs gradually: lung cancer, liver damage
      • Cause and effect may not be easily apparent
  • Mixes may be more than the sum of their parts
    • We can’t determine the impact of mixed hazards
      • They may act in ways that cannot be predicted from the effects of each in isolation
    • Synergistic effects = interactive impacts that are more than or different from the simple sum of their constituent effects
      • Mixed toxicants can sum, cancel out, or multiply each other’s effects
      • New impacts may arise from mixing toxicants
  • Risk assessment
    • Risk = the probability that some harmful outcome will result from a given action
      • Exposure to environmental health threats doesn’t automatically produce an effect
      • Rather, it causes some probability (likelihood) of harm
    • Probability entails
      • Identity and strength of threat
      • Chance and frequency that an organism will encounter it
      • Amount of exposure to the threat
      • An organism’s sensitivity to the threat
  • Perceiving risks
    • Everything we do involves some risk
    • We try to minimize risk, but we often misperceive it
      • Flying versus driving
    • We feel more at risk when we cannot control a situation
      • We fear nuclear power and toxic waste, but not smoking or overeating
  • Analyzing risk quantitatively
    • Risk assessment = the quantitative measurement of risk and the comparison of risks involved in different activities or substances
      • It is a way of identifying and outlining problems
    • Several steps:
      • Scientific study of toxicity
      • Assessing an individual or population’s likely extent of exposure to the substance, including frequency, concentrations, and length of exposure
    • Studies are often performed by industry-associated scientists, which may undermine the study’s objectivity
  • Risk management
    • Combines decisions and strategies to minimize risk
    • Scientific assessments are considered with economic, social, and political needs and values
    • Developed nations have federal agencies to manage risk
      • The U.S. has the Centers for Disease Control (CDC), the EPA, and the Food and Drug Administration (FDA)
    • Comparing costs and benefits is hard
      • Benefits are economic and easy to calculate
      • Health risks (costs) are hard-to-measure probabilities of a few people being affected
  • The process of risk management
  • One approach to determining safety
    • Innocent until proven guilty approach: product manufacturers must prove a product is safe
      • Benefits: now slowing down technological innovation and economic advancement
      • Disadvantage: putting into wide use some substances that may later on turn out to be dangerous
  • Another approach to determining safety
    • Precautionary principle approach: the government, scientists, and the public are required to prove a product is dangerous
      • Assume substances are harmful until they are proven harmless
      • Identifies troublesome toxicants before they are released
      • But, this may impede the pace of technology and economic advance
  • Two approaches for determining safety
  • Philosophy affects policy
    • Different nations use different policies; most use a mix between the “innocent until proven guilty” principle and the precautionary principle
      • Europe is shifting more towards the precautionary principle
      • Industries like the “innocent until proven guilty” approach because it allows them to produce more and make more money
  • The EPA regulates many substances
    • Federal agencies apportion responsibility for tracking and regulating synthetic chemicals
      • FDA: food, food additives, cosmetics, drugs, and medical devices
      • EPA: pesticides
      • Occupational Safety and Health Administration (OSHA): workplace hazards
    • Many public health and environmental advocates fear it isn’t enough
      • Many synthetic chemicals are not actually tested
      • Only 10% have been tested for toxicity
      • Fewer than 1% are government regulated
  • International regulation
    • Nations address chemical pollution with international treaties
    • Stockholm Convention on Persistent Organic Pollutants (POPs) was ratified by 140 nations in 2004
      • Ends the release of the 12 most dangerous POPs
    • EU’s Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) Program
      • Aims to evaluate and restrict dangerous chemicals while giving industries a streamlined regulatory system
      • It will cost the chemical industry 2.8 – 5.2 billion euros (U.S. $3.8 – 7.0 billion), but will save more than 10 times that in health benefits
  • Conclusion
    • International agreements represent a hopeful sign that governments are working to protect society, wildlife, and ecosystems from toxic chemicals and environmental hazards
    • Once all the scientific results are in, society’s philosophical approach to risk management will determine what policies are enacted
    • A safe and happy future depends on knowing the risks that some hazards pose and on replacing those substances with safer ones
  • QUESTION: Review
    • Which of the following is a biological hazard?
      • Earthquake
      • Smoking
      • Virus
      • A pesticide
      • All are biological hazards
  • QUESTION: Review
    • A “vector” is defined as …
      • A highly toxic, radioactive compound
      • An organism that transfers pathogens to a hose
      • A compound with fire-retardant properties
      • A compound that mimics natural substances
  • QUESTION: Review
    • Toxicity is …
      • The study of the effects of poisonous substances
      • Any toxic agent
      • Any substance that causes environmental degradation
      • The degree of harm a substance can cause
  • QUESTION: Review
    • A “teratogen” causes…?
      • Cancer
      • Mutations
      • Birth defects
      • Problems in the hormonal system
  • QUESTION: Review
    • Why is research into endocrine disrupters controversial?
      • Negative findings threaten the industry’s economics
      • Research is still only beginning
      • Much research is funded by industry
      • All of these are reasons why research is controversial
  • QUESTION: Review
    • A human-based study that compares a group of smokers to non-smokers to determine the effects of smoking is …
      • An epidemiological study
      • A case study
      • Not likely to be funded
      • Not going to tell about future risks
  • QUESTION: Interpreting Graphs and Data
    • Our perception, and the reality, of risk often do not match. Given this graph (reality), and your knowledge of sources of anxiety (perception), which statement is correct?
      • Smoking is very dangerous and we are very anxious about it
      • Smoking is not dangerous, but we are very anxious about it
      • Airplane accidents are dangerous, and we are very anxious about it
      • Airplane accidents are not dangerous, but we are very anxious about it
  • QUESTION: Interpreting Graphs and Data
    • If the “low” dose = 5 units of a chemical, the “medium” dose = 10 units, and the “high” dose = 15 units, how much of the chemical is required to kill 50% of the study population?
    From The Science behind the Stories
    • About 5 units
    • About 10 units
    • About 15 units
    • You can’t tell from the graph
  • QUESTION: Viewpoints
    • Is it unethical for a country that has banned a chemical to manufacture and export it to other countries?
      • Yes; if we won’t have it in the U.S., we shouldn’t make it
      • Yes, but the money we get from selling it will help our economy
      • No; let people decide what they want to do
      • No; in fact, chemicals should not be banned in the U.S. either
  • QUESTION: Viewpoints
    • Should the government follow the precautionary principle and force industries to prove their products are safe?
      • Absolutely; it is up to industry to prove its chemicals are safe
      • Maybe, if it is not too expensive
      • No; let the government and scientists prove a chemical is dangerous before it is taken off the market
      • No, as long as the product makes money and jobs for the industry, it should be allowed